The present invention relates to generally a thermal printer of the type in which the current is made to flow through a resistor so as to generate heat thereby blackening in a desired pattern a thermally sensitive paper located in closely spaced-apart relation with the thermal head to print desired characters and more particularly to a device for use with a thermal printer of the type described for controlling the density of characters to be printed.
In some small-sized electronic computers such as desk-top calculators, operands and the results of operation are generally indicated by a number of displaying tubes or the like arrayed in one row on the computer. In another kind of computer printers are additionally incorporated so that operands or numerals to be operated and the results of operation may be printed upon a rolled paper or paper tape. Such printers have an advantage in that the operands or numerals to be operated may be visually recognized and checked and the results of operation may be permanently recorded so that the printers are widely used. Of various types of printers, a thermal printer is particularly advantageous because it has no mechanical components and the number of movable parts may be minimized.
As its name implies, the thermal printer utilizes heat to print alphanumeric symbols or any other characters (hereinafter referred to as "characters" for simplicity) on a thermally sensitive paper so that it is desirable to adjust the density of characters to be printed in response to the environmental temperature, the thermal characteristics of thermo-sensitive paper, the aging thereof, the preference of an operator and the like.
One of the objects of the present invention is therefore to provide a device simple in construction and operation for adjusting the density of characters to be printed on a thermo-sensitive paper.
Another object of the present invention is to provide a device simple both in construction and operation for adjusting the density of characters to be printed for use with a printer of the type employing a thermal head which is driven by the pulse signals derived by the frequency division of the clock pulses.
Another object of the present invention is to provide a device simple both in construction and operation for adjusting the density of characters to be printed for use with a thermal printer of the type employing a thermal head comprising a plurality of dot elements.
Another object of the present invention is to provide a device simple both in construction and operation for adjusting the density of characters to be printed for use with a thermal printer of the type employing a thermal head comprising a plurality of dot elements and a character generating circuit for selecting a predetermined combination of dot elements to be driven.